Ultra-low power (ULP) transmitters are key subsystems for wireless sensor networks and internet-of-things (IoT). The system lifetime, however, is severely limited by their power consumption and available battery technology. The two most power hungry components of modern day transceivers are the oscillators, i.e. the digitally control oscillator (DCO), and the power amplifier (PA). Energy harvesting techniques, which are now enjoying more widespread use, can enable further applications but typically provide lower supply voltages than the deep-nanoscale CMOS supply of 1V. For example, on-chip solar cells typically generate about 0.2 to 0.8V. Although dc-dc converters can boost harvester output voltage, the poor efficiency (≦80%) of most of these converters introduces a significant power penalty and wastes much of the harvested energy.
Therefore, RF oscillators as well as power amplifiers as two of the most power hungry blocks in the transceiver must be very power efficient and preferably operate directly at the output of the energy harvester. There is thus a need for a transmitter switching current source oscillator topology and power amplifier topology that is suitable for use in ULP applications.